Numerous techniques have been proposed in the past for the formation of composite articles wherein fiber reinforcement is provided within a matrix of a polymeric material. Heretofore such composite articles commonly have been prepared wherein the matrix is a highly cross-linked thermosetting resin. During the formation of such composite articles the fibrous material commonly is impregnated with a liquid comprising the neat or dissolved uncured or partially-cured thermosetting resin to form a pliable, tacky prepreg which is subsequently placed in the desired configuration and is cured to a predetermined solid form over an extended period of time. The drapable and tacky nature of such prepregs has greatly aided in their use when forming composite articles having a complex configuration since adjoining plies tend to adhere well to each other and stay in place during the composite formation process. Such resulting thermosetting prepregs commonly must be used promptly following their manufacture or stored under refrigeration so as to eliminate problems resulting from the premature curing of the same.
When attempts have been made to dissolve thermosetting resins in a solvent and to impregnate a fibrous material followed by evaporation of the solvent, difficulties commonly have been encountered. For instance, some thermosetting resins are not readily soluble thereby making uniform impregnation difficult to achieve. Complete solvent removal commonly has been a problem and contributes to void formation in the resulting composite article. Also, the solvent may be injurious to workers in the area unless special and often costly procedures are used to provide the requisite worker protection.
Blends of reinforcing fibers and thermoplastic fibers have been proposed for use in the formation of composite articles wherein the thermoplastic fibers are melted to form the matrix phase. Such blends inherently lack tack which is useful during layup to form a fiber-reinforced composite article.
Reference also can be found in the literature to providing the matrix-forming thermosetting resin or thermoplastic polymer as small solid particles which are mixed with the fibrous material prior to composite formation. Heretofore, such proposals have not become a commercial reality primarily because of the inability to achieve uniform impregnation of the fibrous reinforcement, the tendency of the particles to further segregate within the fibrous material and to separate from the fibrous material, and the necessity to melt the particles following placement among the fibers so as to immobilize the same. Such fusion has resulted in the formation of a stiff boardly product which lacks tack and is largely unsuitable for use in the formation of a composite article having a complex configuration. Also, when the particle impregnation is not uniform, the matrix will not be uniformly dispersed among fibers in the resulting composite article. This will result in a void product having resin-rich and resin-lean areas and unpredictable non-uniform mechanical properties.
British Pat. No. 1,264,432 concerns the application of a dispersion of particles of a thermoplastic polymer to newly spun glass fibers.
British Pat. No. 1,424,168 concerns the formation of a stiff sheet or tape prepreg wherein fibers are contacted with a bath containing water, thickening agent, and thermosetting resin or thermoplastic polymer particles which immediately thereafter are melted at a temperature between 60.degree. to 100.degree. C. to cause the particles to adhere to the fibers. Uniform fiber impregnation would not be achieved and the stable tacky and pliable product of the present invention would not result.
U.S. Pat. No. 4,292,105 concerns the impregnation of a fibrous material from a bath of the specified composition containing water, thickener, and thermosetting resin or thermoplastic polymer particles. The conditions described would not achieve uniform impregnation to produce a quality prepreg. Also, in the working examples the product would have no drapability since it was heated to fuse the polymer.
U.S Pat. No. 4,626,306 concerns the impregnation of a fibrous lap with particles of a thermosetting resin or thermoplastic polymer by dipping in a bath containing the particles in the absence of a binding agent. Uniform fiber impregnation would not be achieved and the stable tacky and pliable product of the present invention would not result.
U.S. Pat. No. 4,680,224 makes reference to the impregnation of fiber strands with a poly(arylene sulfide) powder or a slurry of such powder. The patent is devoid of teachings concerning how such impregnation can be accomplished in the improved manner contemplated herein or how one could provide the improved product of the present invention.
Copending U.S. Ser. No. 114,362, filed Nov. 4, 1987, of Robert Dyksterhouse and Joel A. Dyksterhouse is entitled "Production of Improved Preimpregnated Material Comprising A Particulate Thermoplastic Polymer Suitable For Use In The Formation Of A Substantially Void-Free Fiber-Reinforced Composite Article", and sets forth a technique for forming a tacky and drapable fibrous material which uniformly incorporates particles of thermoplastic polymer.
Copending U.S. Ser. No. 147,153, filed Feb. 5, 1988, of Alan C. Handermann and Edward D. Western is entitled "Improvements in the Formation of Preimpregnated Material Comprising Particulate Thermoplastic Polymer Suitable for Use in the Production of a Substantially Void-Free Fiber-Reinforced Composite Article Having Improved Transverse Properties", and sets forth a technique for improving the transverse properties of the resulting composite article which comprises a matrix of a thermoplastic polymer.
It is an object of the present invention to provide a method for the formation of an improved preimpregnated fibrous material suitable for the formation of a substantially void-free thermoset composite article comprising a plurality of adjoining substantially parallel reinforcing fibers.
It is an object of the present invention to provide an improved method for impregnating a fibrous material with solid particles of a matrix-forming thermosetting resin in a uniform and consistently reliable manner.
It is an object of the present invention to provide an improved method for producing a preimpregnated fibrous product suitable for use in the production of composite articles having solid particles of matrix-forming thermosetting resin substantially uniformly dispersed between adjoining filaments in a uniform and stable manner in the absence of fusion bonding.
It is an object of the present invention to provide a method for producing an improved preimpregnated product containing solid particles of thermosetting resin substantially uniformly dispersed among adjoining filaments which is drapable and tacky at ambient conditions, is handleable without segregation of the particles within the fibrous material, and which upon the application of heat and pressure can be transformed into a substantially void-free thermoset composite article of a predetermined configuration.
It is an object of the present invention to provide an improved method for producing a preimpregnated fibrous material suitable for use in the production of a composite article wherein reinforcing fibers are provided in a matrix of a thermoset resin with no solvent being present when the resin it is introduced among the reinforcing fibers.
It is an object of the present invention to provide an improved preimpregnated fibrous material suitable for use in the formation of a composite article comprising a fiber-reinforced thermoset resin which in preferred embodiments is capable of being substantially fully cured on a more expeditious basis.
It is an object of the present invention to provide an improved impregnated fibrous material suitable for use in the formation of a composite article comprising a fiber-reinforced thermoset resin which in preferred embodiments is capable of being substantially fully cured in the substantial absence of the generation of a volatile by-product.
It is an object of the present invention to provide an improved preimpregnated fibrous material which exhibits an extended shelf life at ambient conditions in the absence of refrigeration and is suitable for use in the formation of a fiber-reinforced thermoset resin.
It is a another object of the present invention to provide an improved preimpregnated fibrous material suitable for use in the formation of a fiber-reinforced substantially void-free composite article and which exhibits a combination of highly desirable characteristics as discussed herein including drapability, handleability without adverse consequences, and tack.
It is a further object of the present invention to provide an improved preimpregnated fibrous material suitable for use in the formation of high performance fiber-reinforced parts for use in aircraft, spacecraft, industrial machinery and automotive applications.
These and other objects, as well as the scope, nature and utilization of the present invention, will be apparent to those skilled in the art from the following detailed description and appended claims.